If you happen to use the argument "sslfingerprint" in your fetchmailrc then make sure you get comcast's new ssl string. Otherwise fetchmail will not pop your mail. The fetchmail line you need to use is below.
Secondly, make sure you have the latest fetchmail (around fetchmail v6.3.8) because of comcast is using Maillennium and it has lots-o-bugs. Below is a from a fetchmail info page and FAQ.
# INCOMPATIBLE CHANGE * Automatically disable the POP3 TOP command if the greeting string contains "Maillennium POP3/PROXY server", which is used by comcast and known to truncate messages after 80 kByte. Fall back to RETR, and complain if we had used TOP otherwise (the warning is printed only once per server in daemon mode). Suggested by Ed Wilts. *Note* that this means messages are marked read on these servers, which is a deviation from how 6.3.1 behaved, but we have no alternative, comcast haven't fixed this bug in years. Preventing the loss of the remainder of the message justifies this incompatible fix. I8. How can I use fetchmail with comcast.net or other Maillennium servers? Stock fetchmail will work with a Maillennium POP3/PROXY server... but this server will truncate "TOP" responses after 64 - 82 kB (we have varying reports), in violation of Internet Standard #53 aka. RFC-1939 (POP3). Don't mistake this for a fetchmail bug. (Reported July 2003.) Comcast documented they haven't understood what this is about in two messages from April 2004. Beginning with version 6.3.2, fetchmail will fall back to the RETR command if the greeting string contains "Maillennium POP3/PROXY server", and print a warning message. This means however that fetchmail has no means to prevent the "seen" flag from being set on the server (Note that officially, POP3 has no notion of seen tracking, but it works for some sites.) Workaround for older versions: use the fetchall option.
The above info was found here.